Method of scale inhibition

ABSTRACT

A method is disclosed to inhibit scale formation in aqueous systems whereby a threshold amount of a scale inhibiting agent, represented by an aminoacid alkylphosphonic acid, is added to the aqueous system. The aminoacid moiety can be represented by α-species or by species having, at least, two or more carbon atoms between the carboxylic moiety and the amine group. These aminoacid based inhibitors exhibit unusually superior performance and system acceptability compared to leading state-of-the-art inhibitors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Non-Provisionalapplication Ser. No. 12/376,896, filed May 14, 2009, which claims thebenefit of priority from International PCT Application No.PCT/EP07/004,682 filed on May 25, 2007, and European Patent ApplicationNo. 6016597.4 filed on Aug. 9, 2006. The disclosures of InternationalPCT Application No. PCT/EP07/004,682 and European Patent Application No.6016597.4 are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to an improved method of scale inhibition, suchas barium scale inhibition, which can be useful in connection with oilrecovery and water treatment applications. The method broadly comprisesthe addition of a threshold amount of a selected amino acid alkylphosphonic acid scale inhibitor. The scale inhibitor, for use in theinventive method, can be selected from α-amino acid alkyl phosphonicacids and from amino acid species having a C₂-C₂₀ hydrocarbon groupconnecting the carboxyl and amine moieties. Excluded are specificα-amino acid alkyl phosphonic acids, namely those which are substitutedby: selected electron rich moieties containing, at least, one lone pairof electrons; aromatics wherein at least one of the carbon atoms hasbeen substituted by a heteroatom; and compounds wherein the α-carbonatom is substituted by narrowly defined electron withdrawing moieties.

The domain of effectively controlling the formation of inorganicdeposits, in particular inhibiting the formation of undesirable levelsof the like deposits, including frequently calcium carbonate and bariumsulphate, in water is well known and has been around for a long time. Asone can consequently expect, the relevant art is fairly crowded.

WO 01/49756 discloses scale inhibitors comprising a hydro solublecopolymer consisting of major amounts of styrene sulfonic acid and vinylsulfonic acid and, optionally, minor levels of non-ionizable monomers.These inhibitor combinations can be used in a squeeze treatment. U.S.Pat. No. 5,112,496 describes compositions and methods for inhibiting oilfield scale formation, particularly in high brine environments.Aminomethylene phosphonates containing 2 or more amine moieties, whereinsubstantially all of the available N—H functions have been phosphonated,are suitable for use. U.S. Pat. No. 4,080,375 pertains to methylenephosphonates of amino-terminated oxyalkylates, having at least two aminogroups, and the use thereof as scale inhibitors in marine oil recoveryactivities as well as their use for chelation in biological systems. Asan example, the phosphonates can effectively sequester iron ions withinthe context of secondary oil recovery by means of water floods.

U.S. Pat. No. 5,263,539 describes method and composition technologyuseful for controlling and reducing the occurrence of scale insubterranean formations. The inhibitor compositions comprise an aminophosphonic acid and a copolymer of an alkenyl sulfonic acid compound andan ethylenically unsaturated monomer. The phosphonic acid can berepresented by bishexamethylene triamine pentamethylene phosphonic acid.GB 2 306 465 pertains to a method of scale inhibition for use in oilfield operations where water can contain high concentrations of alkalineearth metal salts such as barium salts. Preferred scale inhibitors canbe represented by hydroxyl alkylated phosphonomethyl amines.

U.S. Pat. No. 6,022,401 discloses biodegradable corrosion inhibitors andanti-scalants for use in oil field fluid systems and other industrialwater applications. The corrosion inhibitors/anti-scalants arerepresented by modified poly(aspartic acid) polymers and modifiedaspartic acid units. The modified aspartic acid can be substituted byselected side chains such as methyl phosphonic acids/salts.

EP 0 408 297 describes scale inhibitors suitable for inhibiting calciumand barium scale formation in aquatic systems in which iron can bepresent. The inhibitor is represented by a methylene phosphonate,preferably carboxybisnitrilo tetra(methylene phosphonic acid), alsoknown as urea(tetramethylene phosphonic acid). WO 01/85616 divulges ascale- and corrosion-inhibitor for application, inter alia, in waterused in oilfield activities, containing, at least, one oxyalkylene unitand one phosphonate unit. The oxyalkylene can be represented bytriethylene glycol or tetraethylene glycol. The phosphonate can berepresented by vinyl phosphonic acid or vinylidene diphosphonic acid. Ina preferred approach, the phosphonate and the oxyalkylene constituentscan be reacted to thus yield a single compound for use.

Kulin Huang et al., Eur. J. Inorg. Chem. 2004, 2956-2960, describe thesynthesis of functionalized γ-zirconium phosphate-phosphonates based onN-phosphonomethyl-L-proline from proline andN-phosphonomethyl-1,3-thiazolidine-4-carboxylic acid from cysteine. Amethod for producing N-phosphonomethylglycine by reaction ofhexahydrotriazine with triacyl phosphate is described in WO 2003 000704.Along the same lines, DDR patent 141 930 describes the manufacture ofmonophosphonated amino acids or the esters thereof. The amino acidmoiety can, in the final product, be represented by α-alanine,β-alanine, phenylalanine and asparagine. The purpose of the study wasthe preparation of monophosphonates having one residual N—H function.

DE 41 31 912 discloses mixtures of carboxyalkane aminomethane phosphonicacids prepared by reacting natural proteins, in particular from wastesuch as e.g. leather, corn and soya, egg white, skimmed and sugar-freemilk powder, wool and silk waste, animal hair and other protein wastes.U.S. Pat. No. 5,087,376 discloses a method of inhibiting the formationof scale-forming salts by means of a low level of diphosphonomethylderivatives of taurine or cysteic acid.

U.S. Pat. No. 5,414,112 discloses N-bis(phosphonomethyl) amino acids andtheir use to control calcium carbonate scale in contact with industrialprocess waters. Specific compounds described areN,N-bis(phosphonomethyl)-L-glutamic acid,N,N-bis(phosphonomethyl)-L-serine andN,N,N′,N′-bis(phosphonomethyl)-L-lysine. The L-lysine compound isrepresented by species carrying one phosphonomethyl moiety attached toone amino radical.

The art, in essence, aims at adding cumulative functionalities to thussecure additive results without providing remedy to known performancedeficiencies, particularly within the context of marine oil recoveryactivities and/or water treatment applications, and/or avoiding multicomponent systems which are known to exhibit material deficiencies whichare inherently attached to such known active combinations.

DETAILED DESCRIPTION

It is a major object of this invention to provide a beneficial methodfor scale inhibition capable of effectively limiting scale in aqueousenvironment under a broad range of conditions including temperature,hardness levels and alkalinity. It is another object of this inventionto provide an effective scale control method thereby substantially usinga single active scale inhibitor. Another object of the invention aims atproviding effective oil scale control without any substantial secondarynegatives in relation to e.g. the medium of application. Still anotherobject of this invention aims at providing effective means for watertreatment control. Yet another object of this invention concerns aprovision of scale control under severe temperature conditions.

The foregoing and other objects of this invention can now be met by theprovision of a scale inhibition method comprising the use of thresholdamounts of selected alkyl phosphonated amino acids.

The term “percent” or “%” as used throughout this application stands,unless defined differently, for “percent by weight” or “% by weight”.The terms “phosphonic acid” and “phosphonate” are also usedinterchangeably depending, of course, upon medium prevailingalkalinity/acidity conditions. The term “threshold” is well known in thewater treatment domain. The ability of very small amounts of scaleinhibitors to keep large quantities of scalants in solution is known asthe “threshold effect”. Or in other words, it is the prevention ofprecipitation from supersaturated solutions of scalants by ppm levels ofinhibitor. The term “ppm” stands for “parts per million”.

A beneficial method for effectively controlling the formation ofinorganic deposits, in particular the inhibition of earth alkali metalscale, has now been discovered. In more detail, the method in accordancewith this invention concerns scale control in aqueous systems adding athreshold amount of a scale inhibiting agent selected from the group of:

i. aminoacid alkylphosphonic acids having the formulaA¹-(B)_(x)

-   wherein A¹ has the formula    HOOC-A-NH₂-   wherein A is independently selected from C₂-C₂₀ linear, branched,    cyclic or aromatic hydrocarbon chains, optionally substituted by    C₁-C₁₂ linear, branched, cyclic or aromatic hydrocarbon groups,    optionally substituted by OH, COOH and/or NH₂ moieties, and-   B is an alkylphosphonic acid moiety having from 1 to 6 carbon atoms    in the alkyl group and x is an integer of from 1 to 10, preferably    from 1 to 6,    ii. aminoacid alkylphosphonic acids having the formula    A²-B_(y)-   wherein A² has the formula    HOOC—C(NH₂)(R)(R′)-   wherein R and R′ are independently selected from C₁-C₂₀ linear,    branched, cyclic or aromatic hydrocarbon chains, optionally    substituted by C₁-C₁₂ linear, branched, cyclic or aromatic    hydrocarbon groups, optionally substituted by OH, NH₂ and/or COOH,    and one of R or R′ can be hydrogen-   with the proviso of excluding:-   compounds wherein R and/or R′ are electron rich moieties containing,    at least, one lone pair of electrons, which moiety is directly    attached to an aromatic moiety by a covalent bond; or-   aromatics wherein at least one of the carbon atoms has been    substituted by a heteroatom; and compounds, in the event R is    —C(X)(R″)(R′″) and R, R″ and R′″ are hydrogen wherein X is an    electron withdrawing group selected from NO₂, CN, COOH, SO₃H, OH and    halogen,-   with the further proviso that when:-   A² is L-lysine, at least one L-lysine amino radical carries 2 (two)    alkyl phosphonic acid moieties; and when-   A² is L-glutamic acid, the term glutamic acid phosphonate represents    a combination of from 50-90% by weight pyrrolidone carboxylic acid    N-methylene phosphonic acid and from 10-50% by weight of L-glutamic    acid diphosphonic acid, expressed on the basis of the reaction    products; and-   B is an alkylphosphonic acid moiety having from 1 to 6 carbon atoms    in the alkyl group and y is an integer in the range of from 1 to 10,    preferably from 1 to 6,

A first essential aminoacid alkylphosphonic acid for use in the methodof this invention can be represented by the formula:A¹-(B)_(x)

-   wherein A¹ has the formula    HOOC-A-NH₂-   wherein A is independently selected from C₂-C₂₀ linear, branched,    cyclic or aromatic hydrocarbon chains, (said chains being)    optionally substituted by C₁-C₁₂ linear, branched, cyclic or    aromatic hydrocarbon groups, (said groups and/or chains being)    optionally substituted by OH, COOH and/or NH₂ moieties. In a    preferred execution, A can be represented by a C₂-C₁₆ linear    hydrocarbon chain, optionally and preferably substituted by 1 to 3    NH₂ moieties. The selection of any number of carbon atoms in the    hydrocarbon chain can constitute a desirable execution depending    upon the choice of additional optional groups and/or optional    moieties. The actual determination of preferred combinations is a    routine measure, well known in the domain of the technology.

A second essential aminoacid alkylphosphonic acid for use in the methodof this invention can be represented by the formula:A²-B_(y)

-   wherein A² has the formula    HOOC—C(NH₂)(R)(R′)-   wherein R and R′ are independently selected from C₁-C₂₀ linear,    branched, cyclic or aromatic hydrocarbon chains, (said chains being)    optionally substituted by C₁-C₁₂ linear, branched, cyclic or    aromatic hydrocarbon groups, (said groups and/or said chains being)    optionally substituted by OH, NH₂ and/or COOH moieties, and one of R    or R′ can be hydrogen with the proviso of excluding structures which    are not suitable for use within the context of the inventive    technology.

In a preferred execution of the method herein, the aminoacid in thephosphonate inhibitor (ii) can be represented by D,L-alanine wherein yis 2, L-alanine wherein y is 2, L-lysine wherein y is in the range offrom 2 to 4, L-phenylalanine wherein y is 2, L-arginine wherein y is inthe range of from 2-6, L-threonine wherein y is 2, L-methionine whereiny is 2, L-cysteine wherein y is 2 and L-glutamic acid wherein y is 1 to2.

It was found that the L-glutamic acid alkylene phosphonic acid compoundas such is, because of insufficient performance and stability, notsuitable for use in the method of this invention. Depending upon theformation reaction conditions, the L-glutamic acid alkylene phosphonicacid resulting from the methylenephosphonation of L-glutamic acid can berepresented by a substantially binary mixture containing, based on themixture (100%), a majority of a mono-methylene phosphonic acid derivedfrom a carboxylic acid substituted pyrrolidone and a relatively smallerlevel of a dimethylene phosphonic acid glutamic acid compound. It wasfound that, in one beneficial embodiment the reaction product frequentlycontains from 50% to 90% of the pyrrolidone carboxylic acid N-methylenephosphonic acid scale inhibitor and from 10% to 50% of the L-glutamicacid bis(alkylene phosphonic acid) compound. The sum of thediphosphonate and monophosphonate inhibitors formed during the reactionfrequently exceeds 80%, based on the glutamic acid starting material.The binary mixture can also be prepared by admixing the individual,separately prepared, phosphonic acid compounds. In another preferredexecution, the L-lysine carrying one alkylene phosphonic acid groupattached to amino radical(s) represents not more than 20 molar % of thesum of the L-lysine carrying one and two alkylene phosphonic acid groupsattached to amino radical(s). In another preferred execution, theL-lysine alkylene phosphonic acid is represented by a mixture ofL-lysine carrying two alkylene phosphonic acid groups attached to(individual) amino radical(s) (lysine di) and L-lysine carrying fouralkylene phosphonic acid groups (lysine tetra) whereby the weight ratioof lysine tetra to lysine di is in the range of from 9:1 to 1:1, evenmore preferred 7:2 to 4:2.

Preferred aminoacids in the phosphonate inhibitors (i) include7-aminoheptanoic acid, wherein x is 2,6-aminohexanoic acid, wherein x is2,5-aminopentanoic acid, wherein x is 2, 4-amino butyric acid, wherein xis 2 and 13-alanine wherein x is 2. Preferred aminoacids in thephosphonate inhibitors (i) can be prepared beneficially starting fromlactams or other conventionally known materials; 7-aminoheptanoic acidcan be used instead of 2-azacyclooctanone to make the correspondingdiphosphonate. The preferred aminoacid starting materials areillustrated in the examples hereinafter. In short, a mixture ofstoichiometric proportions of the starting material aminoacid (1 mole),phosphorous acid (2 moles), aqueous hydrochloric acid (1.2 moles) isheated under stirring to 100° C., the formaldehyde (2 moles) is thengradually added over a period of 120-140 minutes at a temperature in therange of from 100-120° C. The reaction mixture is thereafter kept at105-115° C. for an additional 60-100 minutes. It is understood that thestoichiometric proportions of the starting materials can be varied tomeet the desired degree of phosphonic acid substitution by reaction withthe available N—H functions.

In another preferred execution herein, the scale inhibitor for use inthe method of this invention can be represented by selected combinationsof aminoacid polyphosphonates of this invention in combination with aphosphonic acid selected from the group of: (a) amino(poly)alkylenepolyphosphonic acids wherein the alkylene moiety contains from 1 to 20carbon atoms; (b) hydroxyalkylene polyphosphonic acids wherein thealkylene moiety contains from 2 to 50 carbon atoms; and (c) phosphonoalkane polycarboxylic acids wherein the alkane moiety is in straightchain configuration containing from 3 to 12 carbon atoms. Actuallypreferred are: aminoalkylene polyphosphonic acids having from 1 to 12carbon atoms in the alkylene moiety; hydroxyalkylene phosphonic acidscontaining from 2 to 12 carbon atoms in the alkylene moiety and twophosphonic acid groups; whereas phosphono alkane polycarboxylic acidshave a straight chain alkane configuration having from 4 to 8 carbonatoms and wherein the molar ratio of phosphonic acid radical tocarboxylic acid radical is in the range of from 1:2 to 1:4. Particularlypreferred are polyphosphonic acids having from 2 to 8 phosphonic acidgroups. Individually preferred species were found to include thefollowing: aminotri(methylene phosphonic acid) and its N-oxide;1-hydroxyethylene(1,1-diphosphonic acid); ethylenediaminetetra(methylene phosphonic acid); diethylene triaminepenta(methylenephosphonic acid); hexamethylene diamine tetra(methylenephosphonic acid); hydroxyethyl aminobis(methylene phosphonic acid);N,N′-bis(3-aminopropyl)-ethylenediamine hexa(methylene phosphonic acid);and butane-2-phosphono-1,2,4-tricarboxylic acid.

The ponderal ratio of aminoacid phosphonate to phosphonic acid is in therange of from 98:2 to 25:75, preferably from 90:10 to 50:50.

A² can be represented by α-amino acids including specific natural aminoacids such as e.g. occurring in animal species. Amino acids generallyare the building blocks of proteins. There are over forty known aminoacids about twenty of which are actually contained in e.g. animaltissue. Amino acids can be made by hydrolysis starting from proteins, byenzymatic fermentation and/or by chemical synthesis. This domain of thetechnology is eminently well known and all the individual technologiesare abundantly documented in the literature. Suitable amino acids can beused in their D, D,L, and L forms as well as mixtures of the D and Lforms. Preferred α-amino acids for use in the phosphonate inhibitorsinclude: D,L-alanine; L-alanine; L-phenylalanine; L-lysine; L-arginine;L-methionine; L-cysteine; L-threonine; and L-glutamic acid.

Specific amino acids are excluded as follows:

-   1. α-aminoacids wherein R and/or R′ are electron rich moieties    directly attached to an aromatic moiety. As an example, the reaction    of L-tyrosine (1 eq.) (R=-p-OH Phenyl; R′=H) with H₃PO₃ (2 eq.) and    formaldehyde (2.2 eq.) in the presence of HCl (1.5 moles) between    108 and 112° C. does not lead to the corresponding bis(methylene    phosphonic acid). Indeed, ³¹P NMR analysis only shows signals for    the starting phosphorous acid with traces of phosphoric acid. A    water insoluble product is obtained; it is believed to be due to the    reaction of formaldehyde with tyrosine resulting in the formation of    methylene bridges between aromatic moieties;-   2. α-aminocids wherein R and/or R′ are aromatics wherein at least    one carbon atom has been substituted by a heteroatom. For example,    the reaction of L-tryptophan (1 eq.) with H₃PO₃ (2 eq.) and    formaldehyde (2.2 eq.) in the presence of HCl (2.5 moles) between    107 and 111° C. does not lead to the corresponding bis(methylene    phosphonic acid). ³¹P NMR analysis only shows signals for the    starting phosphorous acid with traces of phosphoric acid. A water    insoluble product is obtained; it is believed to be due to the    reaction of formaldehyde with tryptophan resulting in the formation    of methylene bridges between aromatic moieties; and-   3. α-aminoacids wherein in the event R is —C(X)(R″)(R′″) and R′, R″    and R′″ are hydrogen wherein X is an electron withdrawing group    selected from NO₂, CN, COOH, SO₃H, OH and halogen. As an example,    the reaction of L-aspartic acid (1 eq.) (X═COOH) with H₃PO₃ (2 eq.)    and formaldehyde (2.2 eq.) in the presence of HCl (1.5 moles)    between 110 and 115° C. leads to a complex product mixture    including: fumaric acid; imino-bis(methylene phosphonic acid);    aminotri(methylene phosphonic acid) (ATMP) and L-aspartic acid    bis(methylene phosphonic acid). The latter product has been shown by    ³¹P NMR to decompose under the reaction conditions into fumaric acid    and imino bis(methylene phosphonic acid) which is itself converted    into ATMP. In another example, the reaction of L-serine (1    eq.)(X═OH) with H₃PO₃ (2 eq.) and formaldehyde (2.2 eq.) in the    presence of HCl (1.5 moles) between 107 and 112° C. leads to a    complex product mixture including amino tri(methylene phosphonic    acid) (ATMP) and phosphorous acid. ³¹P NMR does not show signals    corresponding to the L-serine mono- or di-phosphonates. It is    believed that the L-serine phosphonates are unstable and decompose,    under the reaction conditions, ultimately leading to ATMP.

Specific α-aminoacids not suitable for use within the claimed technologyare: tyrosine; tryptophan; asparagine; aspartic acid; and serine.

The amino acid alkylphosphonate scale inhibitors for use in theinventive method can be prepared by reacting one or more of theavailable N—H functions of the aminoacid with phosphorous acid andformaldehyde, in the presence of hydrochloric acid, in aqueous mediumhaving a pH of generally less than 4 by heating that reaction mixture,at a temperature of usually greater than 70° C. for a sufficient time tocomplete the reaction. This kind of reaction is conventional andwell-known in the domain of the technology and examples of the novelphosphonate compounds have been synthesized, as described below, via thehydrochloric acid route.

In a preferred method, the aminoacid phosphonates can be made undersubstantial exclusion of hydrohalogenic acid and correspondingby-products and intermediates. Specifically, the aminoacid phosphonatescan be manufactured in presence of not more than 0.4%, preferably lessthan 2000 ppm, of hydrohalogenic acid, expressed in relation to thephosphorous acid component (100%) by reacting:

-   (a) phosphorous acid;-   (b) an aminoacid; and-   (c) a formaldehyde:-   in reactant ratios of (a): (b) of from 0.05:1 to 2:1; (c): (b) of    from 0.05:1 to 5:1; and (c): (a) of from 5:1 to 0.25:1;-   wherein (a) and (c) stand for the number of moles to be used and (b)    represents the number of moles multiplied by the number of N—H    functions in the amine, in the presence of an acid catalyst having a    pKa equal or inferior to 3.1, said catalyst being homogeneous with    respect to the reaction medium and being used in reactant ratios as    follows:-   (b): (d) of from 40:1 to 1:5;-   wherein (d) stands for the number of moles of catalyst multiplied by    the number of available protons per mole of catalyst, followed by    recovering the aminoacid phosphonates formed in a manner known per    sé.

The catalyst has a pKa equal or inferior to 3.1, preferably equal orinferior to 2.75, most preferably equal or inferior to 1.9, saidcatalyst being homogeneously compatible with the reaction medium. ThepKa can be expressed as follows:pKa=−log₁₀Ka

-   wherein Ka represents the thermodynamic equilibrium acidity    constant.

The term “homogeneous” catalyst means that the catalyst, suitable foruse, forms a single liquid phase within the reaction medium under thereaction conditions. The homogeneous nature of a catalyst can beascertained routinely by e.g. visible inspection of precipitation orphase separation properties.

Preferred catalyst species can be selected from sulphuric acid,sulphurous acid, trifluoroacetic acid, trifluoromethane sulfonic acid,methane sulfonic acid, oxalic acid, malonic acid, p-toluene sulfonicacid and naphthalene sulfonic acid.

The homogenous reaction is preferably conducted at a temperature in therange of from 70° C. to 150° C. with an approach selected from:

-   -   conducting the reaction under ambient pressure with or without        distillation of water and non-reacted formaldehyde;    -   in a closed vessel under autogeneous pressure built up;    -   in a combined distillation and pressure arrangement whereby the        reaction vessel containing the reactant mixture is kept under        ambient pressure at the reaction temperature followed by        circulating the reaction mixture through a reactor operated        under autogeneous pressure built up thereby gradually adding the        formaldehyde and other selected reactants in accordance with        needs; and    -   a continuous process arrangement, possibly under autogeneous        pressure built up, whereby the reactants are continuously        injected into the reaction mixture and the phosphonic acid        reaction products is withdrawn on a continuous basis.

In another preferred method, the aminoacid phosphonates for use hereincan be prepared under substantial exclusion of hydrohalogenic acid,specifically in the presence of not more than 0.4%, preferably less than2000 ppm, of hydrohalogenic acid, expressed in relation to thephosphorous acid component (100%), by reacting: (a) phosphorous acid;(b) an aminoacid; and (c) formaldehyde; in reactant ratios as follows:(a): (b) of from 0.05:1 to 2:1; (c): (b) of from 0.05:1 to 5:1; and (c):(a) of from 5:1 to 0.25:1; wherein (a) and (c) stand for the number ofmoles to be used and (b) represents the number of moles multiplied bythe number of N—H functions in the amino acid, in the presence of aheterogeneous, with respect to the reaction medium, Broensted acidcatalyst selected from the group consisting of:

-   (1) solid acidic metal oxide combinations as such or supported onto    a carrier material;-   (2) cation exchange resins selected from the group comprising    copolymers of styrene, ethyl vinyl benzene and divinyl benzene,    functionalized so as to graft SO₃H moieties onto the aromatic group    and perfluorinated resins carrying carboxylic and/or sulfonic acid    groups;-   (3) organic sulfonic and carboxylic Broensted acids which are    substantially immiscible in the reaction medium at the reaction    temperature;-   (4) an acid catalyst derived from:

(i) the interaction of a solid support having a lone pair of electronsonto which is deposited an organic Broensted acid;

(ii) the interaction of a solid support having a lone pair of electronsonto which is deposited a compound having a Lewis acid site;

(iii) heterogeneous solids functionalized by chemical grafting with aBroensted acid group or a precursor therefore; and

-   (5) heterogeneous heteropolyacids of the general formula    H_(x)PM_(y)O_(z) wherein P is selected from phosphorus and silicon    and M is selected from W and Mo and combinations thereof followed by    recovering the aminoacid alkylphosphonic acid formed in a manner    known per sé.

Examples of suitable Broensted catalysts are fluorinated carboxylicacids and fluorinated sulfonic acids having from 6 to 24 carbon atoms inthe hydrocarbon chain. A specific example of a suitable catalyst isrepresented by perfluorinated undecanoic acid.

In another execution, suitable heterogeous acid catalysts can berepresented by cation exchange resins. Usually such resins comprisecopolymers of styrene, ethylvinyl benzene and divinyl benzenefunctionalized such as to graft SO₃H groups onto the aromatic groups.

These catalysts can be used in different physical configurations such asin gel form, in a macro-reticulated configuration or supported onto acarrier material such as silica, or carbon, or carbon nanotubes. Theheterogeneous Broensted catalyst can be used in many operationalmanufacturing arrangements well known in the domain of the technology.The term “heterogeneous” means that the Broensted catalyst issubstantially insoluble in the reaction medium at the reactionconditions or substantially immiscible, thus liquid, in the reactionmedium at the reaction conditions. The heterogeneous reaction ispreferably conducted at a temperature in the range of from 70 to 150° C.for a time sufficient to complete the reaction.

The essential formaldehyde component is a well known commodityingredient. Formaldehyde generally is produced and sold as watersolutions containing variable, frequently minor, e.g. 0.3-3%, amounts ofmethanol and are reported on a 37% formaldehyde basis. Formaldehydesolutions exist as a mixture of oligomers. Formaldehyde precursors can,for example, be represented by paraformaldehyde, a solid mixture oflinear poly(oxymethylene glycols) of usually fairly short, n=8-100,chain length, and cyclic trimers and tetramers of formaldehydedesignated by the terms trioxane and tetraoxane respectively. Theformaldehyde component can also be represented by aldehydes and ketoneshaving the formula R₁R₂C═O wherein R₁ and R₂ can be identical ordifferent and are selected from the group of hydrogen and organicradicals. When R₁ is hydrogen, the material is an aldehyde. When both R₁and R₂ are organic radicals, the material is a ketone. Species of usefulaldehydes are, in addition to formaldehyde, acetaldehyde, caproaldehyde,nicotinealdehyde, crotonaldehyde, glutaraldehyde, p-tolualdehyde,benzaldehyde, naphthaldehyde and 3-aminobenzaldehyde. Suitable ketonespecies for use herein are acetone, methylethylketone, 2-pentanone,butyrone, acetophenone and 2-acetonyl cyclohexanone.

The phosphorous acid reactant is preferably prepared, in a known manner,under substantial exclusion of halogen, by contacting elementalphosphorus, such as tetraphosphorus, with water at a temperature below200° C., in the presence of a catalyst effective to promote oxidation ofphosphorus, by reaction with water; or by contacting P(V) species with areducing agent, such as hydrogen, in the presence of a reducingcatalyst; or by contacting a hydrolysis feed mixture comprisingphosphate esters and phosphonate esters with liquid water and steam tothereby hydrolyze the phosphonate esters to phosphorous acid.

The syntheses of examples of the amino acid phosphonates herein aredescribed.

165.19 g (1 mole) of L-phenyl alanine are mixed with a solution of 164 g(2 moles) of phosphorous acid in 147.8 g of 37% aqueous hydrochloricacid (1.5 moles) and 250 cc of water. The mixture is heated understirring to 110° C. 180.5 g of a 36.6% aqueous solution (2.2 moles) offormaldehyde are added over a period of 110 minutes while maintainingthe reaction temperature between 106° C. and 107° C. Upon completion ofthe formaldehyde addition, the reaction mixture is maintained, for anadditional 90 minutes, at a temperature of 107° C. to 108° C. ³¹P NMRanalysis of the crude product showed the presence of 68% of L-phenylalanine bis(methylene phosphonic acid).

131.17 g (1 mole) of L-isoleucine are mixed with a solution of 164 g (2moles) of phosphorous acid in 147.8 g of 37% aqueous hydrochloric acid(1.5 moles) and 150 cc of water. The mixture is heated under stirring to110° C. 180.5 g of a 36.6% aqueous solution of formaldehyde (2.2 moles)are added over a period of 100 minutes while maintaining the reactiontemperature at 110° C. Upon completion of the formaldehyde addition, thereaction mixture is maintained at 110° C. for an additional 110 minutes.³¹P NMR analysis of the crude product showed the presence of 69.7% ofL-isoleucine bis(methylene phosphonic acid).

131.17 g (1 mole) of D,L-leucine are mixed with a solution of 164 g (2moles) of phosphorous acid in 147.8 g of aqueous hydrochloric acid (1.5moles) and 150 cc of water. The mixture is heated, under stirring, to105° C. 180.5 g of a 36.6% aqueous solution of formaldehyde (2.2 moles)are then added over a period of 100 minutes while maintaining thereaction temperature between 105° C. and 110° C. Upon completion of theformaldehyde addition, the reaction mixture is maintained at 110° C. foran additional 60 minutes. ³¹P NMR analysis of the crude product showedthe presence of 69.7% of D,L-leucine bis(methylene phosphonic acid).

117.15 g (1 mole) of L-valine are mixed with a solution of 164 g (2moles) of phosphorous acid in 147.8 g of 37% hydrochloric acid (1.5moles) and 150 g of water. The mixture is heated, under stirring, to110° C. 180.5 g of 36.6% aqueous formaldehyde (2.2 moles) are added in85 minutes while maintaining the reaction temperature at 107° C. Uponcompletion of the formaldehyde addition, the reaction mixture ismaintained at 107° C. for an additional 60 minutes. ³¹P NMR analysis ofthe reaction product, as is, showed the presence of 70.3% of L-valinebis(methylene phosphonic acid).

85 g (1 mole) of 2-pyrrolidone are mixed with a solution of 164 g (2moles) of phosphorous acid in 118.4 g of 37% hydrochloric acid (1.2moles) and 100 g of water. The mixture is heated, under stirring, to100° C. 172.1 g of 36.6% aqueous formaldehyde (2.1 moles) are added overa period of 135 minutes while maintaining the reaction temperaturebetween 100° C. and 114° C. Upon completion of the formaldehydeaddition, the reaction mixture is maintained at 110° C. for anadditional 90 minutes. ³¹P NMR analysis of the reaction product, as is,showed the presence of 91.2% of 4-amino butanoic acid bis(methylenephosphonic acid).

113.1 g (1 mole) of ε-Caprolactam are mixed with 164 g (2 moles) ofphosphorous acid in 118.4 g of 37% aqueous hydrochloric acid (1.2 moles)and 100 g of water. The mixture is heated, under stirring, to 100° C.172.1 g of 36.6% aqueous formaldehyde (2.1 moles) are added over aperiod of 105 minutes while maintaining the reaction temperature between100° C. and 112° C. Upon completion of the formaldehyde addition, thetemperature of the reaction mixture is maintained, for an additional 75minutes, at a temperature of 110° C. ³¹P NMR analysis of the reactionproduct showed the presence of 89% of 6-amino hexanoic acidbis(methylene phosphonic acid).

92.27 g (0.65 mole) of 2-Azacyclononanone are mixed with 106.6 g (1.3moles) of phosphorous acid in 96.07 g of 37% aqueous hydrochloric acid(0.97 mole) and 65 g of water. The mixture is heated, under stirring, to100° C. 114 g of 36.6% aqueous formaldehyde (1.39 moles) are then addedin 70 minutes while maintaining the reaction temperature between 104° C.to 106° C. Upon completion of the formaldehyde addition, the temperatureof the reaction mixture is maintained at 107° C. for an additional 60minutes. ³¹P NMR analysis of the reaction product showed the presence of84% of 8-amino octanoic acid bis(methylene phosphonic acid).

89 g (1 mole) of L-alanine are mixed with 164 g (2 moles) of phosphorousacid in 147.81 g of 37% aqueous hydrochloric acid (1.5 moles) and 150 gof water. The mixture is heated, under stirring, to 110° C. 180.51 g of36.6% aqueous formaldehyde (2.2 moles) are then added over a period of120 minutes while maintaining the temperature of the reaction mixturebetween 110° C. and 115° C. Upon completion of the formaldehydeaddition, the temperature of the reaction mixture is maintained at 106°C. for an additional 60 minutes. ³¹P NMR analysis of the reactionproduct showed the presence of 77.6% of L-alanine bis(methylenephosphonic acid).

Arginine was reacted, in a conventional manner, with phosphorous acidand formaldehyde in the presence of hydrochloric acid. The crudereaction was found to be substantially completely, 72.7%, represented bya bis(alkylene phosphonic acid) derivative. This reaction product wasused in the Examples.

91.33 g (0.5 mole) of L-lysine hydrochloride are mixed with 164 g (2moles) of phosphorous acid in 73.91 g of 37% aqueous hydrochloric acid(0.75 mole) and 120 g of water. The mixture is heated, under stirring,to 105° C. 180.51 g of 36.6% aqueous formaldehyde (2.2 moles) are addedover a period of 120 minutes while maintaining the reaction temperaturebetween 106° C. and 109° C. Upon completion of the formaldehydeaddition, the temperature of the reaction mixture is maintained at 106°C. for an additional 50 minutes. ³¹P NMR analysis of the reactionproduct showed the presence of 72.2% of L-lysine tetra(methylenephosphonic acid) and about 14% of 2-amino 6-imino bis(methylenephosphonic acid) hexanoic acid. This preparation was used in theExamples under the name “tetraphosphonate”.

273.98 g (1.5 moles) of L-lysine hydrochloride are mixed with 369 g (4.5moles) of phosphorous acid in 221.72 g of 37% aqueous HCl (2.25 moles)and 400 g of water. The mixture is heated with stirring to 106° C.404.14 g of 36.6% Aqueous formaldehyde (4.95 moles) are added over aperiod of 180 minutes while maintaining the reaction temperature between106 and 112° C. Upon completion of the formaldehyde addition, thereaction mixture is heated for an additional 60 minutes at 110° C. ³¹PNMR analysis of the crude product shows the presence of 52.1% ofL-lysine tetra(methylene phosphonic acid), about 19.7% of2-amino-6-imino bis(methylene phosphonic acid)hexanoic acid and about22% of N-Me L-lysine diphosphonate. This composition corresponds to anapproximate average of 2 methylene phosphonic acid groups per L-lysinemoiety. This preparation was used in the Examples under the name“diphosphonate”.

147.13 g (1 mole) of L-glutamic acid are mixed with a solution of 164 g(2 moles) of phosphorous acid in 147.8 g of 37% aqueous HCl (1.5 moles)and 120 ml of water. This mixture is heated, under stirring, to 110° C.180.5 g of 36.6% Aqueous formaldehyde (2.2 moles) are added over aperiod of 105 minutes while maintaining the reaction temperature around110° C. Upon completion of the formaldehyde addition, the temperature ofthe reaction mixture is maintained at 110° C. for an additional 30minutes. ³¹P NMR analysis of the reaction product shows the presence of20.1% of L-glutamic acid bis(methylene phosphonic acid) and 51.5% of2-pyrrolidone-5-carboxylic acid N-methylene phosphonic acid.

Scale formation, such as carbonate and sulphate scales, can be a majorproblem in oil field production facilities that can result in asignificant well productivity decline. This can, in particular, applywhen sea water is injected into the oil bearing formation to compensatee.g. for a loss in gas pressure. As a result of the presence ofimportant quantities of barium and calcium ions in the down-holeformation water, calcium sulphate and especially barium sulphate andstrontium sulphate can become a major problem in the operation of thewell. Whereas sulphate scales prevail upon seawater injection during theenhanced oil recovery treatment, milder pH conditions, prevailing closerto the surface, pressure differences and high temperatures in thedown-hole formation usually lead to the formation of mixtures ofcarbonate and sulphate scale. The scale inhibitors shall thereforeexhibit performance over a broad range of conditions such as can occurin the oil wells and production facilities. The inhibitor can beintroduced into the oil bearing formation by any suitable treatmentincluding a “squeeze” treatment. In general such a method for oilrecovery requires injecting into a marine oil well an aqueous solutionof the aminoacid phosphonic acid scale inhibitor of this invention in ausual level of from 0.1 to 100000 ppm. Frequently, the production oilwell activity is stopped and the inhibitor solution is injected into theoil well formation. It was established that the scale inhibitors inaccordance with this invention can be used effectively and singly. Thesqueeze treatment generally consists of injecting a scale inhibitorsolution into the wellbore of the producing well to place the inhibitorinto the formation. The scale inhibitor released from the formation ispresent, in the return water, in a concentration of, at least, 0.1,usually at least 0.5, frequently from 10 to 100 ppm to thus exhibiteffective scale control and consequently secure oil well productioncontinuity with levels of inhibitor means reduced by one order ofmagnitude compared to actually prevailing practice.

In more detail, a beneficial method for oil recovery can be done byinjecting into marine oil wells an aqueous solution of the aminoacidphosphonic acid compound of the invention in a level of from 0.1 to100000 ppm. The method can be conducted by continuously injecting intothe well an aqueous solution of from 0.1 to 800 ppm of the aminoacidphosphonic acid compound. The continuous injection frequently means thatthe scale inhibitor solution is injected into the water injection well.However, it is understood that the continuous injection can also applyto the surroundings of the production well such as the well-headarrangement including under-water equipment for example pumps and pipes.The aminoacid scale inhibitors of this invention can also be used insqueeze oil recovery methods. Such squeeze method comprises, insequence: stopping the production wellbore activity; introducing throughthe production wellbore the aqueous treatment solution containing theaminoacid phosphonic acid scale inhibitor in a level of from 100 to100000 ppm; injecting sea water through the production wellbore to placethe scale inhibitor within the targeted area of the formation;restarting the oil extraction activity; and producing return fluids,containing oil and return water, through the production wellbore.

The inventive method also contemplates the use of the aminoacidphosphonic acid inhibitors herein in scale forming water systemscontaining usually more than 100 mg/l of barium and/or strontiumhardness and/or calcium carbonate and having a pH generally within therange of from 2-10. To that effect, of from 0.1 to 800 ppm, preferablyof from 0.2 to 100 ppm, of the aminoacid phosphonate scale inhibitor isadded to the water system.

The individual aminoacid phosphonate scale inhibitors can, in oneexecution, be used substantially singly, or in the event they are usedas a mixture of more than one (i) species or a mixture of more than one(ii) species or as a mixture of (i) and (ii) species, then it wasobserved that one individual inhibitor in accordance with this inventionshall constitute, on a ponderal basis, at least 50%, usually 60% or moreof the mixture of inhibitors of this invention. It was observed thataminoacid mixtures originating from protein hydrolysates are not wellsuitable for use in the method herein due to, inter alia, interactionsof the various species which can adversely affect performance. Preferredscale inhibitors herein, particularly for application within the contextof oil producing wells, shall have a thermal decomposition, measured at140° C., of less than about 10%.

The scale inhibitor performance of the aminoacid alkyl phosphonatessuitable for use in the method of this invention can be quantifiedthereby using comparative testing methods as follows.

Thermal Stability Assessment.

This is a test to assess the thermal stability of phosphonates in thepresence of synthetic North Sea water. The test is carried out bysubmitting mixtures of North Sea water and phosphonates stabilized at pH5.5 to a one week heating at 140° C. The thermal degradation isdetermined by ³¹P NMR analysis. The results give the percentage byweight of product which is decomposed after the treatment.

Test details are as follows:

-   -   prepare an aqueous solution containing 20% of active acid        phosphonate (AA) at pH 5.5 (solution 1);    -   prepare synthetic North Sea water having a pH of 5.5 (solution        2);    -   prepare a sample of 1% active acid phosphonate by mixing 1 g of        solution 1 with 19 g of solution 2;    -   put the sample so prepared in an oven at 140° C. for one week;        and    -   analyze the sample, after the heat treatment, for thermal        decomposition by means of ³¹P NMR spectroscopy.        Brine/Sea Water Compatibility.

This test assesses sea water compatibility of the phosphonates added at:100; 1000; 10000; and 50000 ppm to North Sea water after 22 hours at 90°C. Calcium left in solution is measured by ICP.

Test details are as follows:

-   -   prepare synthetic North Sea water at pH 5.5;    -   add the phosphonate at 100, 1000, 10000 and 50000 ppm active        acid to the synthetic North Sea water solution;    -   prepare 5 blank solutions made by mixing the required amount of        distilled water with North Sea water to obtain the same dilution        as obtained by the addition of 1, 100, 1000, 10000 and 50000 ppm        active acid phosphonate to the synthetic North Sea water        solution;    -   the phosphonate samples with the respective phosphonates at the        4 concentrations as well as the 5 blanks are stored in an oven        at 90° C. for a period of 22-24 hours;    -   upon completion of the test, the samples are observed visually;    -   after completion of the test, the pH values are being carefully        monitored and 50 ml are drawn from each sample, filtered through        a 40 μm Millipore filter and stabilized at pH_(<)2 by addition        of 37% aqueous hydrochloric acid;    -   Ca tolerance values are calculated as follows:

${\%\mspace{14mu}{Ca}\mspace{14mu}{tolerance}} = {\frac{V_{1}}{V_{0}} \times 100}$

where V₀=ppm Ca found in the blank solution; and

V₁=ppm Ca found in the solution with the phosphonate.

Barium Sulphate Scale Inhibition.

This is a static test to evaluate the efficiency of phosphonates inpreventing barium and strontium scale inhibition in oil field scalingconditions. The test is carried out by determining the amount of BaSO₄and SrSO₄ that has precipitated after 22 hours at 90° C. in a 50/50mixture of synthetic North Sea water and Formation water containing thephosphonates to be tested at 5 different concentrations. The amount ofsoluble Ba and Sr ions is determined by ICP. The results stand for theminimum phosphonate concentration for 100% barium sulphate scaleinhibition or give the scale inhibition at 100 ppm loading ofphosphonate.

Test details are as follows:

Synthetic North Sea Water:

Salts mmol/l NaCl 420.1 CaCl₂•2H₂O 10.08 MgCl₂•6H₂O 54.32 KCl 8.7Na₂SO₄•10H₂O 25.8 NaHCO₃ 2.21Formation Water:

Salts mmol/l NaCl 1313 CaCl₂•2H₂O 77.75 MgCl₂•6H₂O 19.74 KCl 11BaCl₂•2H₂O 1.82 SrCl₂•6H₂O 7.53

-   -   synthetic North Sea and Formation water are prepared having a pH        of 6. These water solutions are preheated at 90° C. before        starting the test. An acetic acid/sodium acetate buffer is        prepared and added to the North Sea water in order to give the        required pH;    -   add to a glass bottle the required amount of scale inhibitor to        obtain the test concentrations (15, 30, 50, 70 and 100 ppm        active phosphonic acid) of the scale inhibitor in the final test        mixture;    -   to this glass bottle, add 50 ml of North Sea water while        stirring. Then add to this glass bottle 50 ml of Formation        water;    -   also prepare one blank solution by mixing 50 ml of North Sea        water with 50 ml of Formation water;    -   put the sample bottles in an oven for 22 hours at 90° C.;    -   after 22 hours, take 3 ml of each test solution from the        surface, filter through a 0.45 μM Millipore filter and add to a        stabilizing solution. The samples are then analyzed by ICP for        Ba and Sr;    -   the phosphonate efficiencies as BaSO₄ and SrSO₄ scale inhibition        are calculated as follows:

${\%\mspace{14mu}{Scale}\mspace{14mu}{inhibition}} = {\frac{V_{1} - V_{0}}{V_{2} - V_{0}} \times 100}$where

V₀=ppm Ba (or Sr) found in the blank solution;

V₁=ppm Ba (or Sr) found in the solution with the inhibitor;

V₂=ppm Ba (or Sr) present in the Formation water.

Scale inhibitor phosphonate samples for use in the method of thisinvention were performance tested by means of the foregoing testingprocedures. The performance data were as follows.

EXAMPLES

Ba Scale (***) Ca Tolerance in % N^(o) (ppm) Amino Acid Inhibition 1001000 10000 50000 1 D,L-alanine 97% @ 100 ppm 100 99 94 100 2 L-alanine96% @ 100 ppm 96 90 8 97 3 L-glutamic 31% @ 100 ppm 100 97 99 97 acid 4L-lysine (*) 50 ppm full 100 81 20 98 scale 5 L-lysine (**) 30 ppm full98 86 27 97 scale 6 L-phenyl 10 ppm full 96 76 1 26 alanine scale 7L-isoleucine 85% @ 100 ppm 93 96 44 82 8 L-histidine 90% @ 100 ppm 100100 95 100 9 L-valine 47% @ 100 ppm 97 98 73 80 10 L-arginine 30 ppmfull 97 86 6 61 scale 11 L-threonine 30 ppm full 94 86 22 85 scale 12L-methionine 50 ppm full 96 77 2 31 scale 13 L-cysteine 50 ppm full 9699 91 79 scale 14 β-Alanine 50 ppm full 100 98 89 64 scale 15 4-Amino21% @ 100 ppm 97 99 99 100 butyric acid 16 5-Amino 13% @ 100 ppm 100 9699 100 pentanoic acid 17 6-Amino hexanoic 12% @ 100 ppm 98 100 100 100acid 18 7-Amino heptanoic acid 11% @ 100 ppm 99 100 100 100 (*) =tetraphosphonate; (**) = diphosphonate, (***) expressed as: ppmphosphonate needed for 100% BaSO₄ scale inhibition; or % scaleinhibition for 100 ppm phosphonate.

A series of phosphonate inhibitors were tested for thermal stabilitythereby using the method set forth above. The testing results were asfollows.

Example Thermal Stability at 140° C. N^(o) Amino Acid 1 weekDecomposition in % 19 D,L-alanine 8.2 20 L-alanine 7.9 21 L-glutamicacid 0 22 L-lysine (*) 2.5 23 L-lysine (**) 8.8 24 L-phenylalanine 4.325 D,L-leucine 2.9 26 L-isoleucine 32.3 27 L-valine 19.5 28 L-arginine18.4 29 L-methionine 6.5 30 4-Amino butyric acid 30.0 315-Aminopentanoic acid 10.2 32 6-Aminohexanoic acid 3.5 337-Aminoheptanoic acid 5.4 34 Diethylene triamino 23.6 pentamethylenephosphonate (*) = tetraphosphonate; (**) = diphosphonate.

The performances of a series of aminoacid phosphonate/phosphonic acidscale inhibitor combinations were tested by means of the foregoingtesting procedures. The testing data are summarized in the followingtable. The cumulative weight of the aminoacid phosphonate and thephosphonic acid (ATMP) is 100% e.g. the presence of 30% ATMP means thatthe aminoacid phosphonate represents 70%.

Performance Testing Example Ba Scale (***) Ca Tolerance in % N^(o) Aminoacid ATMP % Inhibition 100 1000 10000 50000* 35 D,L-alanine — 97% @ 100ppm 100 99 94 100 36 D,L-alanine 15 50 ppm full 100 100 71 93 scale 37D,L-alanine 30 15 ppm full 100 98 89 89 scale 38 L-glutamic — 31% @ 100ppm 100 97 99 97 acid 39 L-glutamic 15 100 ppm full 100 100 100 100 acidscale 40 L-glutamic 30 70 ppm full 100 100 100 100 acid scale 41 4-Amino— 21% @ 100 ppm 97 99 99 100 butyric acid 42 4-Amino 15 100 ppm full 9796 100 100 butyric acid scale 43 4-Amino 30 50 ppm full 100 100 97 100butyric acid scale 44 5-Amino — 12% @ 100 ppm 98 100 100 100 pentanoicacid 45 5-Amino 30 70 ppm full 99 98 100 100 pentanoic acid scale 466-Amino — 11% @ 100 ppm 99 100 100 100 heptanoic acid 47 7-Amino 30 50ppm full heptanoic acid scale *= expressed in ppm. (***) as in Examples1-18.

The invention claimed is:
 1. A method for treating water to inhibitscale, such as barium scale, formation which comprises adding athreshold amount of a scale inhibiting agent selected from the group of:i. aminoacid alkylphosphonic acids having the formulaA¹-(B)_(x) wherein A^(l)has the formulaHOOC-A-NH₂ wherein A is independently selected from C₂-C₂₀ linear,branched, cyclic or aromatic hydrocarbon chains, optionally substitutedby C₁-C₁₂ linear, branched, cyclic or aromatic hydrocarbon groups,optionally substituted by OH, COOH and/or NH₂ moieties, and B is analkylphosphonic acid moiety having from 1 to 6 carbon atoms in the alkylgroup and x is an integer of from 1 to 10, and ii. aminoacidalkylphosphonic acids having the formulaA²-B_(y) wherein A² has the formulaHOOC—C(NH₂)(R)(R′) wherein R and R′ are independently selected fromC₁-C₂₀ linear, branched, cyclic or aromatic hydrocarbon chains,optionally substituted by C₁-C₁₂ linear, branched, cyclic or aromaticNH₂ and/or COOH, and one of R or R′ can be hydrogen compounds wherein Rand/or R′ are electron rich moieties containing, at least, one lone pairof electrons, which moiety is directly attached to an aromatic moiety bya covalent bond; or aromatics wherein at least one of the carbon atomshas been substituted by a heteroatom; and compounds, in the event R is—C(X)(R″)(R′″) and R′, R″ and R′″ are hydrogen wherein X is an electronwithdrawing group selected from NO₂, CN, COOH, SO₃H, OH and halogen,with the proviso that compounds are excluded wherein R and R′ are bothhydrogen, with the further proviso that when: A² is L-lysine, at leastone L-lysine amino radical carries 2 (two) alkyl phosphonic acidmoieties; and when A² is L-glutamic acid, the term glutamic acidphosphonate represents a combination of from 50-90% by weightpyrrolidone carboxylic acid N-methylene phosphonic acid and from 10-50%by weight of L-glutamic acid diphosphonic acid, expressed on the basisof the reaction products; and B is an alkylphosphonic acid moiety havingfrom 1 to 6 carbon atoms in the alkyl group and y is an integer in therange of from 1 to
 10. 2. The method in accordance with claim 1 whereinL-lysine carrying one alkylene phosphonic acid group attached to aminoradical(s) represents not more than 20 molar % of the sum of L-lysinecarrying one and two alkylene phosphonic acid groups attached to amineradicals.
 3. The method in accordance with claim 1 wherein the aminoacidin the (ii) aminoacid alkylphosphonic acid is selected from:-D,L-alanine wherein y is 2; -L-alanine wherein y is 2; -L-phenylalaninewherein y is 2; -L-lysine wherein y is in the range from 2 to 4;-L-arginine wherein y is in the range from 2 to 6; -L-threonine whereiny is 2; -L-methionine wherein y is 2; -L-cysteine wherein y is 2; and-L-glutamic acid wherein y is 1 to
 2. 4. The method in accordance withclaim 1 wherein A in the aminoacid phosphonic acid (i) is selected fromC₂-C₁₆ linear hydrocarbon chains substituted by 1 to 3 NH₂ moieties. 5.The method in accordance with claim 1 wherein the aminoacid in the (i)aminoacid phosphonic acid is selected from: -7-aminoheptanoic acid;-6-aminohexanoic acid; -5-aminopentanoic acid; -4-aminobutyric acid; and-β-alanine; whereby x is 2 in each of such species.
 6. The method inaccordance with claim 1 comprising adding to the scale forming watersystem containing more than 100 mg barium and/or strontium hardness perliter, said system having a pH between 2 and 10, from 0.1 to 800 ppm ofthe aminoacid phosphonic acid scale inhibitor.
 7. The method inaccordance with claim 6 wherein of from 0.2 to 100 ppm of the aminoacidphosphonate scale inhibitor is added to the scale forming water system.8. The method in accordance with claim 1 wherein, in addition to theaminoacid alkylphosphonic acid scale inhibitor, a polyphosphonic acid ispresent, said polyphosphonic acid being selected from the group of: (a)aminopolyalkylene polyphosphonic acid whereby the alkylene moietycontains from 1 to 20 carbon atoms; (b) hydroxyalkylene polyphosphonicacids wherein the alkylene moiety contains from 2 to 50 carbon atoms;and (c) phosphono alkane polycarboxylic acids wherein the alkane moietyis in straight chain configuration containing from 3 to 12 carbon atoms;in a ponderal ratio of aminoacid alkyl phosphonic acid to polyphosphonicacid is in the range of from 98:2 to 25:75.
 9. The method in accordancewith claim 8 wherein the polyphosphonic acid is selected from: aminotri(methylenephosphonic acid) and its N-oxide; ethylene diaminetetra(methylenephosphonic acid); diethylene triamine penta(methylenephosphonic acid); hexamethylene diamine tetra(methylene phosphonicacid); hydroxyethyl amino bis(methylene phosphonic acid);N,N′-bis(3-aminopropyl)-ethylenediamine hexa(methylene phosphonic acid);and butane-2-phosphono-1,2,4-tricarboxylic acid; wherein the ponderalratio of aminoacid alkylphosphonic acid to polyphosphonic acid in therange of from 90:10 to 50:50.
 10. The method in accordance with claim 8wherein the aminoacid in the corresponding alkylphosphonic acid isselected from the group of: α-alanine; L-glutamic acid; L-methionine;4-amino butyric acid; 5-aminopentanoic acid; 6-aminohexanoic acid and7-aminoheptanoic acid.
 11. The method in accordance with claim 9 whereinthe aminoacid in the corresponding alkylphosphonic acid is selected fromthe group of: α-alanine; L-glutamic acid; L-methionine; 4-amino butyricacid; 5-aminopentanoic acid; 6-aminohexanoic acid and 7-aminoheptanoicacid.